A wide variety of surfactants and mixtures of surfactants are known for many industrial, commercial and domestic applications. In these uses, there is often a need for the surfactant to be in a pumpable or fluid form for addition to formulations requiring the surfactant since such form enables one to save costs in handling and storing of the composition, as well as ease and convenience in formulating products therewith. Additionally, for numerous reasons, such as formulation flexibility, transportation and storage costs, it is desirable for the surfactant to be available in such pumpable compositions in as high a concentration or proportion of surfactant or active ingredient as possible.
The superior performance of fatty alcohol-based anionic phosphate esters of high monoalkyl phosphate ester content relative to dialkyl phosphate ester content, generally at a ratio of at least 80:20 or more, has long been recognized, especially for their mildness, detergency and foaming properties, and particularly for use in cosmetic or personal care products like shampoos, conditioners and body cleansers. See U.S. Pat. No. 4,139,485 to G. Imokawa et al., issued Feb. 13, 1979. Their usefulness in the latter products is due, at least in part, to their ability to produce high detergency with low skin irritancy compared to other surfactants, such as alkyl sulphates, alkyl ether sulphates, polyoxyethylene alkyl sulphates, alkyl benzene sulphonates and the like. Moreover, such fatty alcohol-based anionic phosphate ester surfactants of high monoalkyl ester content provide surfactants that evidence an excellent balance of properties. For example, as the monoalkyl phosphate content increases relative to the dialkyl phosphate content, the solubility, foaming ability and detergency increase. Additionally, the increase in monoalkyl phosphate content reduces the skin irritancy effect.
The ability to utilize surfactant compositions of high monoalkyl phosphate content in formulation of products has not been without difficulties. It is readily recognized that it is highly desirable that such surfactant compositions be high in active ingredient content, that is, have a high solids content of phosphate ester salts. However, in attempting to produce surfactant compositions of high concentration of phosphate ester salts, it was discovered that the compositions sometimes became rigid or immovable, non-flowable or non-pumpable gels rather than easily handled fluid solutions. Additionally, sometimes phase separation occurred when attempting to produce such high solid content phosphate ester salt surfactant compositions or during subsequent storage periods. In most instances it has been impossible to produce fluid or pumpable phosphate ester salt compositions above about 30 to 40% by weight active ingredient.
In order to address these drawbacks, various approaches have previously been employed. For example, it has been suggested to employ a mixture of different surfactants, such as, for example, as disclosed in U.S. Pat. Nos. 4,753,754 and 5,139,781. Another approach has been to formulate aqueous solutions of such surfactants with generally large amounts of alcohols or other co-solvents, such as propylene glycol, dipropylene glycol or ethanol, which act as thinners and solubilizing agents thereby lowering the viscosity of the solution and inhibiting the formation of a non-flowable gel. However, for preparation of many formulations, it is not desirable to employ surfactant mixtures; in fact, their use is to be avoided because they unnecessarily complicate the formulation process. Especially in cosmetic or personal care product formulations, there is a need, in numerous cases, to bar the use of alcohol or other co-solvent components in the formulations.
Moreover, other previously suggested approaches, such as to utilize alkanolamine salts of mono- or di- alkyl phosphates, or the co-use of alkyl sulfates or sulfonate salt surfactants has introduced other undesirable, irritating ingredients or reduces the desirable properties of the phosphate surfactants.
It is, therefore, desirable that surfactant compositions having high concentrations of alkyl phosphate salt surfactants in stable, pumpable liquid form be available that do not require the presence of such undesirable other surfactants or large amounts of co-solvents or alcohols and minimum amounts of adulterating additives, inactive or performance reducing components. It is further desirable that such surfactant compositions of high concentration of alkyl phosphate surfactants be available in aqueous form for use in cosmetic and personal care products.
A further object of this invention is to provide such stable, pumpable or flowable aqueous surfactant compositions that are pumpable at low temperatures. A further object of this invention is to provide a highly concentrated, pumpable or flowable alkyl phosphate salt surfactant composition, high in monoalkyl phosphate esters relative to dialkyl phosphate esters, that is transparent, preferably clear and colorless, is readily prepared and retains its good solubility, foamability and detergency properties and provides desirable foam density, stability and good skin feel properties. A still further object of this invention is to provide such highly concentrated aqueous surfactant compositions of essentially monoalkyl phosphate ester salts of low residual starting alcohol and phosphoric acid content.
Yet, another object of this invention is to provide such a stable, pumpable liquid surfactant composition with a maximum percent active concentration and a minimum amount of adulterating additives, inactive components or performance reducing components.